1. Field of the Invention
The present invention relates to a metallic cylinder head gasket without a spacing layer. In particular, it concerns a cylinder head gasket with only one functional layer.
2. Related Art
A cylinder head gasket ensures impermeability to gas between the cylinder block and cylinder head. Thereby, the cylinder head gasket must balance elastic vibrations between the cylinder head and cylinder block.
The functional principle of metallic gaskets for cylinder head use in internal combustion engines is that an elastic sealing zone is present. The gasket is designed with beads, which form elastic sealing zones around the area of the combustion chamber. The pressure of the bead adjusts constantly in the operation of the engine based upon the varying stress. The strength of the material layer and also the particular molding of the bead has influence on the elastic properties of the bead, i.e. the elasticity or spring stiffness. The corresponding stress-strain characteristics can only be varied over a narrow area. The area of such a gasket directly surrounding the combustion chamber is exposed to higher stresses during the operation of the engine. To guarantee an adequate sealing in these exposed areas it is necessary to apply a high surface pressure. This is usually achieved by increasing the material strength at the boundary of the combustion chamber, and can be effected by the crimping of a metal layer or by the use of additional layers which are joined with a metal layer of the gasket. Frequently this thickness of material is arranged so that the beads are protected beforehand in the built-in state, to be completely flattened by the pressure.
Cylinder head gaskets usually consist of several layers and also an annular support designated as a stopper. For the increase of pressure in the areas intensely affected, the beads are provided around the combustion chamber, which increases the material thickness.
DE 101 01 604 A1 describes a cylinder head gasket with two sealing layers, one a spacing layer and one an annular support. With this gasket, the main bead is provided with additional supporting beads in the sealing layer, near the combustion chamber.
DE 100 29 352 A1 discloses a gasket in which a metal ring is welded to a metal layer along a welding bead, so that the metal ring and metal layer are kept in a spaced apart relationship to one another. While this gasket has a high impermeability to gas for reason of the welding, the elasticity is reduced due to the firm connection and fixed spacing.
DE 197 51 293 A1 describes a gasket in which a turned-over fold constitutes a pressure confinement for the bead. Thereby, it forms an area of higher pressure. But here the bead is held in indirect force closure, so that the maximum pressure occurs not in the area of the bead, but in the area of the crimping. This sealing principle is followed for diesel engines.
As a rule, a varying construction is used with gasoline engines of passenger cars, whereby the pressure on a boundary is eliminated. Here, the combustion chamber is surrounded only by the beads of the cylinder head gasket, which are flattened in the built-in state. The beads lie here in a direct force fit and thereby receive the maximum pressure.
In this location an uncoiling with great oscillation amplitude takes place with stress, that is, upon impact of pressure through the combustion passage into the combustion chamber. With a conventional gasket it progresses to strong vertical oscillations. Nevertheless, in order for an adequate impermeability to gas to be ensured, a high pressure is generated against the bead. If the bead positioned in direct force fit is not supported, and thus endures the entire stress, the lifetime of the gasket is thereby negatively influenced.
In EP 0574166 B1 a combination of both forms of construction is disclosed. A gasket is described which includes a support ring, which in the built-in state reaches up to full bead of the sealing layer. In this arrangement the bead lies in direct force fit. This arrangement is particularly suitable for engines in which the bridge width between individual combustion chambers is small, and a concentration of the maximum pressure upon the area bordering the combustion chamber is possible.
This support ring follows in its form the profile of the bead, and does not outreach the crest of the bead. Thereby, the spring characteristic of the bead is influenced such that the bead becomes harder and also loses elasticity. In the built-in state an extreme pressure peak also prevails in the area of the crest of the bead. In comparison with a bended beam construction, the support ring, to all intents and purposes, constitutes the support point. With the impact of pressure an uncoiling effect over the crest of the bead develops, which leads to high oscillation amplitudes in the vertical direction. This effect can intensify, depending upon pressure in the combustion chamber.
A support ring designated as a stopper serves to enlarge the material thickness in the area of the bead and thereby the pressure is raised at the most stressed positions of the gasket.
The more layers are used, the more complex and therefore the more expensive the manufacture of a corresponding cylinder gasket head will become. The adjustment of the different layers to one another, and the possible different temperature dependent expansions signify a potential deterioration of the sealing properties and lifetime of the corresponding gasket.